The present invention relates generally to perlite insulation boards and more particularly to a perlite insulation board having gypsum as an essential ingredient and method of making the gypsum-containing board.
Perlite insulation boards have been and continue to be successful products of the roofing industry as insulation under a built-up roof. A typical perlite insulation board includes expanded perlite as its main ingredient, organic fiber (for example, newsprint) and binder (for example, asphalt and starch). An insulation board of this type is described in U.S. Letters Patent 3,042,578 issued to Paul S. Denning on July 3, 1962.
An actual commercially successful perlite insulation board of the type discussed above is manufactured by Johns-Manville Corporation under the trademark "FESCO". This board, which consists essentially of perlite, newsprint fiber, asphalt and possibly starch has a dry weight density of approximately 10 lbs./ft..sup.3. Its coefficient of thermal conductivity (k value) is approximately 0.376. Other physical characteristics include modulus of rupture (MR), interlaminar strength and water absorption resistance. Standard FESCO board has an MR of between 50 psi and 60 psian interlaminar strength of between 6 psi and 10 psi, and water absorption resistance of between 1% and 2% (by volume) for short-term absorption (2 hrs.) and between 20 and 24% (by volume) for long-term absorption (more than 3 weeks).
The physical characteristics just discussed are of primary import in making FESCO insulation board or, for that matter, any other commercially available perlite insulation board, a commercially successful board for its intended use as roof insulation. It must have a sufficiently low K value to provide adequate insulation at not unreasonable thicknesses. It must be relatively light in weight so as to be easily installed in the field and yet it must be sufficiently strong so as to resist damage during installation in the field or enroute. Further, the insulation board should be somewhat resistant to water since it may likely be exposed to the elements, at least between the time it is installed and eventually covered by, for example, a built-up roof.
One standard way in which perlite insulation board of the type described is made is by a continuous wet forming process utilizing a Fourdrinier machine. A dilute aqueous slurry including the expanded perlite, fiber and binder is prepared and deposited in the headbox of the Fourdrinier. At the headbox, the slurry is moved on to a moving screen so as to form a wet mat from the slurry solids. This wet mat is dewatered and moved (generally to a remote location) where residual moisture is driven off, typically by means of external heat provided within an even or dryer.
As will be seen hereafter, one feature of the present invention resides in a perlite insulation board which is more economical than the standard board discussed above, from the standpoint of material costs, and yet a board which at least approximately meets the physical characteristics discussed above, actually surpassing some of the physical characteristics of the standard board discussed above. As will also be seen, this is accomplished by replacing much of the perlite and fiber in the board for less expensive gypsum.
Another feature of the present invention resides in an improved method of making perlite insulation board, made possible through the use of gypsum and making possible (1) a substantial cost reduction in the capital equipment required in manufacturing the board and/or (2) making possible an uncomplicated and economical conversion from an existing gypsum board producing facility to a perlite insulation board producing facility. With regard to this latter point, there are many similarities between these two types of facilities, i.e., a gypsum producing facility and a perlite board producing facility, which make it possible to even consider such a conversion. However, there is one specific difference to be discussed below which makes it impossible to readily convert a standard gypsum facility into a standard perlite insulation board facility without particular expensive equipment changes.
A typical method of making gypsum board includes forming a gypsum slurry and depositing this slurry on a moving belt between continuous sheets of gypsum paper, typical cover sheets for gypsum board. After the gypsum slurry is deposited between these sheets, it is formed into the final product. Eventually it is moved to a drying oven, generally at a remote location from where the slurry is formed and dewatered. In moving this "green" board to the oven, spaced rollers are generally provided. These rollers, which are quite expensive, are generally spaced from 6 to 12 inches apart.
It has been found that the 6 to 12 inch distance between rollers, just discussed, is sufficiently close for the green gypsum board to easily span in its movement from one roller to another without the board sagging therebetween. However, perlite board having the standard ingredients discussed above and made by the method generally discussed cannot span rollers 6 inches apart while in a green state, i.e., between the time the perlite board is dewatered and the time it reaches the dryer. Standard perlite board facilities use rollers which are spaced, at most, approximately 4 inches apart. This is the specific difference between a standard gypsum board facility and a standard perlite insulation board facility referred to above. Hence, to convert the gypsum facility to a perlite board facility requires an increased number of rollers so as to get the standard green perlite board from the dewatering section of the forming machine to the dryer, both of which could be used in the conversion.
As will be seen, applicants have substantially minimized, if not eliminated, this expensive drawback by providing a perlite insulation board which, is a green state, can span rollers spaced 6 inches apart but which, at the same time, retains the important physical characteristics necessary to make the board a commercially successful product for its intended use as roof insulation. In this regard, with the present invention in mind, conversion from a gypsum facility to a perlite insulation board producing facility becomes especially economically attractive since generally the gypsum ore is located in the approximate vicinity of the facility. Hence, the gypsum which, as stated, replaces much of the perlite and fiber, is substantially less expensive (without taking into account freight) than either perlite or news (with or without taking into account freight).